Targeting cIAP2 in a novel senolytic strategy prevents glioblastoma recurrence after radiotherapy

Glioblastomas (GBM) are routinely treated with high doses of ionizing radiation (IR), yet these tumors recur quickly, and the recurrent tumors are highly therapy resistant. Here, we report that IR-induced senescence of tumor cells counterintuitively spurs GBM recurrence, driven by the senescence-associated secretory phenotype (SASP). We find that irradiated GBM cell lines and patient derived xenograft (PDX) cultures senesce rapidly in a p21-dependent manner. Senescent glioma cells upregulate SASP genes and secrete a panoply of SASP factors, prominently interleukin IL-6, an activator of the JAK-STAT3 pathway. These SASP factors collectively activate the JAK-STAT3 and NF-kB pathways in non-senescent GBM cells, thereby promoting tumor cell proliferation and SASP spreading. Transcriptomic analyses of irradiated GBM cells and the TCGA database reveal that the cellular inhibitor of apoptosis protein 2 (cIAP2), encoded by the BIRC3 gene, is a critical survival factor for senescent glioma cells. Senescent GBM cells not only upregulate BIRC3 but also induce BIRC3 expression and promote radioresistance in non-senescent tumor cells. We find that SMAC mimetics targeting cIAP2 act as novel senolytics that trigger apoptosis of senescent GBM cells with minimal toxicity towards normal brain cells. Finally, using both PDX and syngeneic mouse models of GBM, we show that the SMAC mimetic birinapant, administered as an adjuvant therapy after radiotherapy, can eliminate senescent GBM cells and prevent the emergence of recurrent tumors. Taken together, our results clearly indicate that significant improvement in GBM patient survival may become possible in the clinic by eliminating senescent cells arising after radiotherapy Total RNA was extracted from GBM cells LN229 and A172 mock-irradiated and radiation-induced senescent cells.. Three biological replicates of mock-irradiated and IR-induced senescent cells were analyzed by bulk-RNAseq .

胶质母细胞瘤（Glioblastomas, GBM）常规接受高剂量电离辐射（Ionizing Radiation, IR）治疗，但此类肿瘤会快速复发，且复发瘤具有极强的治疗抗性。本研究报道，辐射诱导的肿瘤细胞衰老会反常地促进GBM复发，其驱动机制为衰老相关分泌表型（Senescence-Associated Secretory Phenotype, SASP）。我们发现，经辐射处理的GBM细胞系及患者来源异种移植瘤（Patient Derived Xenograft, PDX）培养物会以p21依赖的方式快速发生衰老。衰老的胶质瘤细胞会上调SASP相关基因，并分泌一系列SASP因子，其中以白细胞介素IL-6（IL-6）——JAK-STAT3信号通路的激活因子——最为突出。上述SASP因子可共同激活非衰老GBM细胞内的JAK-STAT3与核因子κB（NF-κB）信号通路，进而促进肿瘤细胞增殖与SASP表型的扩散。对辐射处理的GBM细胞及癌症基因组图谱（The Cancer Genome Atlas, TCGA）数据库的转录组分析显示，由BIRC3基因编码的细胞凋亡抑制蛋白2（cellular inhibitor of apoptosis protein 2, cIAP2）是衰老胶质瘤细胞的关键存活因子。衰老的GBM细胞不仅会上调BIRC3的表达，还可诱导非衰老肿瘤细胞表达BIRC3并增强其辐射抗性。我们发现，靶向cIAP2的SMAC模拟物可作为新型衰老细胞清除剂，触发衰老GBM细胞的凋亡，且对正常脑细胞的毒性极低。最后，通过GBM的PDX模型与同基因小鼠模型，我们证实，在放疗后作为辅助治疗施用的SMAC模拟物比里纳帕（Birinapant）可清除衰老的GBM细胞，从而防止肿瘤复发。综上，本研究结果明确表明，通过清除放疗后产生的衰老细胞，有望在临床中显著改善GBM患者的生存结局。本研究从假照射及辐射诱导衰老的LN229与A172两株GBM细胞中提取总RNA，对假照射组与IR诱导衰老组的细胞各设置3次生物学重复，采用批量RNA测序（bulk-RNAseq）进行分析。